A digestibility study was conducted with Ross broilers to determine the additivity of apparent or standardized amino acid digestibility values for corn, soybean meal, or a mixture of corn and soybean meal supplemented, with either phytase, protease, or a combination of phytase and protease. A total of 12 experimental diets and a nitrogen-free diet were also fed.   Apparent and standardized amino acid digestibility values were assessed on day 28 post-hatch.

The results indicated that the addition of protease or the combination of protease and phytase increased (P <0.05) the digestibility of amino acids in corn and soybean meal.   This study demonstrates that the effect of exogenous protease and phytase on amino acid digestibility in complete diets is predictable based on measurements made in individual ingredients.  In addition to improving digestibility values, exogenous protease and phytase may enhance precision in least cost formulation systems.